Measurement of Polystyrene Mean Inner Potential by Transmission Electron Holography of Latex Spheres

1998 ◽  
Vol 4 (2) ◽  
pp. 146-157 ◽  
Author(s):  
Y.C. Wang ◽  
T.M. Chou ◽  
M. Libera ◽  
E. Voelkl ◽  
B.G. Frost
Keyword(s):  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Polystyrene Spheres ◽  
Reconstruction Procedure ◽  
A Value ◽  
Transmission Electron ◽  
Phase Images ◽  
The Mean ◽  
Beam Damage

This study describes the use of transmission electron holography to determine the mean inner potential of polystyrene. Spherical nanoparticles of amorphous polystyrene are studied so that the effect of specimen thickness on the phase shift of an incident electron wave can be separated from the intrinsic refractive properties of the specimen. A recursive four-parameter χ-squared minimization routine is developed to determine the sphere center, radius, and mean inner potential (Φ0) at each pixel in the phase image. Because of the large number of pixels involved, the statistics associated with determining a single Φ0 value characteristic of a given sphere are quite good. Simulated holograms show that the holographic reconstruction procedure and the χ-squared analysis method are robust. Averaging the Φ0 data derived from ten phase images from ten different polystyrene spheres gives a value of Φ0PS = 8.5 V (σ) = 0.7 V). Specimen charging and electron-beam damage, if present, affect the measurement at a level below the current precision of the experiment.

The mean inner potential of GaN measured from nanowires using off-axis electron holography

2005 ◽  
Vol 892 ◽  
Author(s):  
Andrew See Weng Wong ◽  
Ghim Wei Ho ◽  
Rafal E Dunin-Borkowski ◽  
Takeshi Kasama ◽  
Rachel A Oliver ◽  
...  
Keyword(s):  
Cross Section ◽  
Carbon Film ◽  
Circular Cross Section ◽  
Electron Holography ◽  
Amorphous Coating ◽  
Gan Nanowires ◽  
A Value ◽  
Accurate Knowledge ◽  
Transmission Electron ◽  
The Mean

AbstractThe mean inner potentials of wurtzite GaN nanowires are measured using off-axis electron holography in the transmission electron microscope (TEM). The nanowires have a circular cross-section and are suspended across holes in a holey carbon film, resulting in an accurate knowledge of their thickness profiles and orientations. They are also free of the implantation and damage that is present in mechanically-polished ion-milled TEM specimens. The effect of a thin amorphous coating, which is present on the surfaces of the nanowires, on measurements of their mean inner potential is assessed. A value for the mean inner potential of GaN of (16.7 ± 0.3) V is obtained from these samples.

Electron holography in materials science

1991 ◽  
Vol 49 ◽  
pp. 670-671
Author(s):  
Hannes Lichte ◽  
Edgar Voelkl
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Materials Science ◽  
Fourier Spectrum ◽  
Object Wave ◽  
Electron Holography ◽  
Reconstruction Procedure ◽  
Numerical Reconstruction ◽  
Transmission Electron ◽  
Unique Interpretation

The object wave o(x,y) = a(x,y)exp(iφ(x,y)) at the exit face of the specimen is described by two real functions, i.e. amplitude a(x,y) and phase φ(x,y). In stead of o(x,y), however, in conventional transmission electron microscopy one records only the real intensity I(x,y) of the image wave b(x,y) loosing the image phase. In addition, referred to the object wave, b(x,y) is heavily distorted by the aberrations of the microscope giving rise to loss of resolution. Dealing with strong objects, a unique interpretation of the micrograph in terms of amplitude and phase of the object is not possible. According to Gabor, holography helps in that it records the image wave completely by both amplitude and phase. Subsequently, by means of a numerical reconstruction procedure, b(x,y) is deconvoluted from aberrations to retrieve o(x,y). Likewise, the Fourier spectrum of the object wave is at hand. Without the restrictions sketched above, the investigation of the object can be performed by different reconstruction procedures on one hologram. The holograms were taken by means of a Philips EM420-FEG with an electron biprism at 100 kV.

Electron holography of catalysts

1995 ◽  
Vol 53 ◽  
pp. 416-417
Author(s):  
A. K. Datye ◽  
D. S. Kalakkad ◽  
L. F. Allard ◽  
E. Völkl
Keyword(s):  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Scale ◽  
Nano Particles ◽  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Information ◽  
Particle Structure

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.

Electron Refraction of Amorphous Nanospheres

1997 ◽  
Vol 3 (S2) ◽  
pp. 1055-1056
Author(s):  
Y.C. Wang ◽  
T.M. Chou ◽  
M. Libera
Keyword(s):  
Refractive Index ◽  
Electron Scattering ◽  
Unit Volume ◽  
High Energy ◽  
Covalent Bonding ◽  
Electron Holography ◽  
High Energy Electron ◽  
Electron Wave ◽  
Transmission Electron ◽  
The Mean

The phase shift imparted to an incident high-energy electron wave in a TEM is related to the specimen’s electron-refractive properties. These, in turn, are related to the electrostatic potential and, by Fourier transform (1), to the electron scattering factors fei(s) for the various atom species i in the specimen and scattering vectors s. The average refractive index is determined by the mean electrostatic (inner) potential, Φo, and can be modelled as Φo = (C/Ω) Σfei(s0) [equation 1] where C = 47.878 (V-Å2) and the summation runs over all of the atoms in the unit volume Ω (2). Calculated fei(s) data are available from the literature (e.g. 3). These calculations have only been done for neutral atoms and some fully ionized cations and anions. They do not account for electron redistribution due to covalent bonding to which Φo is quite sensitive (4).This research is making Φo measurements using transmission electron holography. Holograms were collected using a 200keV Philips CM20 FEG TEM equipped with a non-rotatable biprism (5) and a Gatan 794 Multiscan camera.

Introduction to electron holography

1994 ◽  
Vol 52 ◽  
pp. 396-397
Author(s):  
M. R. McCartney
Keyword(s):  
Spherical Aberration ◽  
Phase Changes ◽  
Phase Image ◽  
Objective Lens ◽  
Phase Plate ◽  
Electron Holography ◽  
Imaging Method ◽  
Electron Sources ◽  
Transmission Electron ◽  
Magnetic Potentials

Electron holography is an imaging method in the transmission electron microscope (TEM) whereby the phase and amplitude of the electron wavefront can be obtained separately, unlike the conventional image which represents the intensity of the electron wave without any direct phase information. In particular, the phase image allows for the possibility of directly imaging the electric and magnetic potentials within a sample on the basis of phase changes produced on the incident electron wavefront. There are many advantages to directly imaging the phase structure and specific examples of the unique information available will be shown. For example, once the phase image is obtained it is possible to correct for the phase changes imposed by the transfer function of the objective lens by directly applying an inverse phase plate.Electron holography was originally proposed in 1949 by Gabor as a means of improving the resolution of electron micrography by correction of spherical aberration but was never fully utilized due to inadequate electron sources. In recent years, the availability of reliable field emission guns as coherent electron sources has stimulated renewed interest in the technique.

Off-Axis Electron Holography of Self-Assembled Co Nanoparticle Rings

2007 ◽  
Vol 1026 ◽  
Author(s):  
Takeshi Kasama ◽  
Rafal E. Dunin-Borkowski ◽  
Michael R. Scheinfein ◽  
Steven L. Tripp ◽  
Jie Liu ◽  
...  
Keyword(s):  
Room Temperature ◽  
Phase Image ◽  
Objective Lens ◽  
Electron Holography ◽  
Zero Field ◽  
Transmission Electron ◽  
Out Of Plane ◽  
Self Assembled ◽  
Magnetic States

AbstractWe use off-axis electron holography in the transmission electron microscope (TEM) to study magnetic flux closure (FC) states in self-assembled nanoparticle rings that each contain between five and eleven 25-nm-diameter Co crystals. Electron holograms are acquired at room temperature in zero-field conditions after applying chosen magnetic fields to the samples in situ in the TEM by partially exciting the conventional microscope objective lens. Mean inner potential contributions to the phase shift are determined by turning the samples over, and subsequently subtracted from each recorded phase image to obtain magnetic induction maps. Our results show that most nanoparticle rings form FC remanent magnetic states, and occasionally onion-like states. Although the chiralities (the directions of magnetization) of the FC states are determined by the shapes, sizes and positions of the constituent nanoparticles, reproducible magnetization reversal of each ring can be achieved by using an out-of-plane magnetic field of between 1600 and 2500 Oe.

Accurate measurements of mean inner potential of crystal wedges using electron holography

1992 ◽  
Vol 50 (1) ◽  
pp. 134-135
Author(s):  
M. Gajdardziska-Josifovska ◽  
M. R. McCartney ◽  
J. K. Weiss
Keyword(s):  
Phase Change ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Electron Wave ◽  
Flat Surfaces ◽  
Numerical Reconstruction ◽  
Digital Holograms ◽  
The Mean ◽  
Energy Dependent ◽  
Magnetic Electron

The phase of an electron wave which has interacted with a material is measured in electron holography experiments with respect to a coherent reference wave which has travelled through vacuum. In non-magnetic electron-transparent materials, and under kinematical diffracting conditions, the phase change (Δφ) of the transmitted electron wave depends only on the thickness (t) and the mean inner potential (Ui) of the material: Δφ = c |Ui| t; c being an energy-dependent constant. This phase change measured from electron holograms has been used previously to determine the mean inner potential of amorphous and polycrystalline films of known thicknesses. Refraction effects in RHEED patterns have also been used to determine the mean inner potential of several crystals with flat surfaces. The reported accuracies in these studies have ranged from 2.5% to 9.5%, although uncertainties in specimen thickness and the unknown effects of surface contamination and/or reconstruction are very likely sources of systematic errors. This paper shows that numerical reconstruction of digital holograms, combined with use of cleaved crystal wedges, enables measurement of the mean inner potential of crystals with enhanced accuracy.

The Comparative Ultrastructure of Fibrin Induced by Thrombin and by Staphylocoagulase

1975 ◽  
Vol 34 (01) ◽  
pp. 223-235 ◽  
Author(s):  
M. J. S King ◽  
M. S Morris ◽  
M Tager
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
T Test ◽  
Test Analysis ◽  
A Value ◽  
Transmission Electron ◽  
The Mean ◽  
Comparative Ultrastructure

SummaryFibrin induced by the action of thrombin and by staphylocoagulase was studied by transmission electron microscopy.Periodic striations were consistently observed in the negatively stained preparations of both fibrins. When 4200 major periods in the thrombin fibrin system were measured the mean length was 228 Å. For 3666 major periods in the coagulase fibrin system the mean length was 223 Å. While the T test analysis of these values gave a value of 10, it is noteworthy that the differences are well within the scatter of periodicity reported in the literature for thrombin-induced fibrin.Gross inspection of the preparations indicated that the coagulase-induced fibrin had a knottier appearance and was accompanied by a greater amount of background debris than the thrombin-induced fibrin.

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